Attach kind information to found usages

[mkaput]

Problem

We are not setting the kind of found reference in textDocument/documentHighlight responses: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#documentHighlightKind

Proposed Solution

Add a kind field to FoundUsage struct and plumb it into textDocument/documentHighlight response.

The value of the kind field should be inferred as a separate step while/just before building FoundUsage instance. This should be fairly easy to infer from the AST location itself:

1. If usage is a binding in let pat = ... statement, or function/closure parameter (or similar) → kind = Write.
2. If usage is in doc comment → kind = Text
3. Otherwise, → kind = Read.

Notes

No response